Method for etching protective film, method for producing template, and template produced thereby

ABSTRACT

A substrate having a protective film formed on a front surface and a recess in a back surface opposite the front surface is prepared. A resist pattern is formed on the protective film. The protective film is etched using plasma while applying a bias voltage, using the resist pattern as a mask. The bias voltage is increased according to the manner of decrease in the dielectric constant of a region of the substrate corresponding to a covered region of the front surface at which the protective film is present.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of PCT InternationalApplication No. PCT/JP2014/001827, filed on Mar. 28, 2014, which claimspriority under 35 U.S.C. §119(a) to Japanese Patent Application No.2013-071643 filed on Mar. 29, 2013. Each of the above applications ishereby expressly incorporated by reference, in its entirety, into thepresent application.

BACKGROUND

The present disclosure is related to a method for etching a protectivefilm formed on a substrate using plasma. The present disclosure is alsorelated to a method for producing a template that utilizes theprotective film etching method and to a template which is produced bythe method for producing a template.

In recent years, films having patterns of protrusions and recesses ofphoto masks for exposure and hard masks for etching, for example, areoften produced by etching protective films formed by materials such aschromium or chromium oxide provided on substrates using plasma,accompanying decreases in processing dimensions.

The intensity of bias voltages in etching processes varies depending onthe states of etching apparatuses during etching. Therefore, JapaneseUnexamined Patent Publication No. 2007-193037, for example, disclosessuppressing changes in a bias voltage in an etching process based on anaperture ratio of a pattern to be formed in the surface of a substrateand a predicted value of changes in reactance.

SUMMARY

However, in the method of Japanese Unexamined Patent Publication No.2007-193037, there is a problem that changes in bias voltage cannot beappropriately suppressed with respect to etching of substrates havingrecesses on surfaces opposite surfaces which are to be utilized in themanufacture of nanoimprinting templates.

Specifically, when etching a substrate having a recess in the backsurface thereof, the surface electrical potential differs at the regionwhere the recess is present and at regions where the recess is notpresent. That is, when a template is produced using a substrate having arecess in the back surface thereof, in the production of templates thatoften involve forming patterns of protrusions and recesses in localizedregions, changes in bias voltage at these local regions cannot bepredicted appropriately if the average reactance of the entire substrateis considered as in Japanese Unexamined Patent Publication No.2007-193037 (paragraph 21 of Japanese Unexamined Patent Publication No.2007-193037).

The present disclosure has been developed in view of the abovecircumstances. The present disclosure provides a method for etching aprotective film that enables the formation of high quality patterns ofprotrusions and recesses on protective films formed on substrates havingrecesses on the back surfaces thereof, and a method for producing atemplate.

Further, the present disclosure provides a method for producing atemplate that utilizes the above etching method and a template which isproduced by the method for producing a template.

A method for etching a protective film of the present disclosurecomprises:

preparing a substrate having a protective film formed on a front surfaceand a recess in a back surface opposite the front surface;

forming a resist pattern on the protective film; and

etching the protective film using plasma while applying a bias voltage,using the resist pattern as a mask;

the bias voltage being increased according to the manner of decrease inthe dielectric constant of a region of the substrate corresponding to acovered region of the front surface at which the protective film ispresent.

In the method for etching a protective film of the present disclosure, aconfiguration may be adopted wherein the bias voltage is increasedaccording to a degree of decrease in the dielectric constant while thedielectric constant is decreasing, and maintained at a valuecorresponding to a constant value while the dielectric constant is atthe constant value. Alternatively, a configuration may be adopted,wherein the bias voltage is zero while the dielectric constant isdecreasing, then increased to a value corresponding to a constant valuewhile the dielectric constant is at the constant value.

In addition, in the method for etching a protective film of the presentdisclosure, the range of the covered region may be detected duringetching, and the manner of decrease in the dielectric constant may bedetermined based on the manner of change in the percentage of the recesswithin the region of the substrate corresponding to the covered region.

In addition, in the method for etching a protective film of the presentdisclosure, plasma components may be measured by plasma emissionspectroscopy during etching, and the manner of decrease of thedielectric constant may be determined based on the manner of change inthe amount of a component which is correlated with etching of theprotective film from among the measured components.

In addition, in the method for etching a protective film of the presentdisclosure, the manner of increase of the bias voltage may be determinedin advance based on the relationship between etching time and the mannerof decrease of the dielectric constant during etching, and the biasvoltage may be increased according to the determined manner of increaseof the bias voltage.

In addition, in the method for etching a protective film of the presentdisclosure, it is preferable for the percentage of metal materialswithin the constituent material of the protective film to be 40% orgreater.

In addition, in the method for etching a protective film of the presentdisclosure, it is preferable for the transmittance of the protectivefilm with respect to light having a wavelength of 365 nm to be 30% orgreater.

A method for producing a template of the present disclosure comprises:

etching a protective film formed on a substrate having a recess on theback surface thereof by the method for etching a protective filmdescribed above; and

etching the substrate using the etched protective film as a mask.

A template of the present disclosure is characterized by being producedby the method for producing a template described above.

The method for etching a protective film of the present disclosureincreases the bias voltage according to the manner of decrease in thedielectric constant of a region of the substrate corresponding to acovered region of the surface of the substrate at which the protectivefilm is present. Therefore, changes in bias voltage at local regions ofthe surface of the substrate at which patterns of protrusions andrecesses are formed can be predicted appropriately and corrected for. Asa result, it becomes possible to form a high quality pattern ofprotrusions and recesses on a protective film formed on a substratehaving a recess on the back surface thereof.

In addition, the method for producing a template of the presentdisclosure utilizes the above method for etching a protective film.Therefore, it becomes possible to form a high quality pattern ofprotrusions and recesses on a protective film formed on a substratehaving a recess on the back surface thereof.

In addition, the template of the present disclosure is produced by theabove method for producing a template. Therefore, the template has ahigh quality pattern of protrusions and recesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a collection of schematic cross sectional diagrams showing thesteps of a method for etching a protective film according to a firstembodiment.

FIG. 2A is a schematic plan view showing a state before reduction of aprotective film during an etching process.

FIG. 2B is a schematic plan view showing a state after reduction of theprotective film during the etching process.

FIG. 3 is a graph showing the manner of decrease of a dielectricconstant and the manner of increase of a bias voltage in the firstembodiment.

FIG. 4 is a collection of schematic cross sectional diagrams showing thesteps of a method for etching a protective film according to a secondembodiment.

FIG. 5 is a graph showing the manner of decrease of a dielectricconstant and the manner of increase of a bias voltage in the secondembodiment.

FIG. 6 is a collection of schematic diagrams, wherein A illustrates astate of plasma etching, and B is a conceptual diagram of an equivalentcircuit at the time of plasma etching when a substrate is considered asa capacitor.

FIG. 7A is a schematic sectional view showing the state of a protectivefilm prior to etching.

FIG. 7B is a schematic sectional view showing a state in which aprotective film range is reduced by etching.

FIG. 8 is a collection of schematic cross sectional diagrams showing thesteps of a conventional method for etching a protective film formed on asubstrate with a recess on the back surface thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the attached drawings. However, the present inventionis not limited to the embodiments to be described below. Note that inthe drawings, the dimensions of the constitutive elements are drawndifferently from the actual dimensions thereof, in order to facilitatevisual recognition thereof.

“Problems of Conventional Technology”

Before describing the embodiments of the present disclosure, challengesin etching a substrate having a recess on the back surface thereof willbe described. A of FIG. 6 is a schematic view showing a state of plasmaetching, and B of FIG. 6 is a conceptual diagram of an equivalentcircuit during plasma etching in which a substrate is considered as acapacitor.

Generally, when forming a pattern on a protective film 21 which isformed on the substrate 20 as a hard mask as shown in FIG. 6, an etchingmethod (reactive ion etching), in which a resist pattern 22 is formed onthe protective film 21, the substrate is placed on the lower electrode23 of an etching container, and plasma P is employed to etch theprotective film 21 using the resist pattern 22 as a mask, is applied. Ametal material such as chromium (Cr), tantalum (Ta), and molybdenumsilicide (MoSi₂), a semiconductor, or compounds thereof is often used asthe material of the protective film 21. At this time, the protectivefilm 21 is a conductor (or a semiconductor), and the substrate 20 is adielectric. Therefore, the substrate 20 and the protective film 21 maybe considered to be a capacitor C with equal electric potential formedon each of the front surface and the back surface of the substrate. Thedielectric constant ε of the capacitor C is determined by the materialof the substrate.

When a negative voltage is applied to the substrate 20 (a bias voltageVb), positive ions X are drawn to the substrate 20 through an ion sheathS based on the potential difference between the surface electricalpotential Vs and the plasma potential Vp generated in the surface of thesubstrate 20 and enter the protective film 21. The plasma potential isdetermined by the generation conditions of the plasma. Therefore, ifplasma generation conditions during the etching remain unchanged, thekinetic energy of the positive ions X will become smaller as larger thesurface electrical potential Vs becomes greater. However, in the casethat a conventional flat substrate 20 is employed, since the surfaceelectrical potential does not change, the kinetic energy of the positiveions X usually does not change over time. In addition, the kineticenergy of the positive ions X that enter the protective film 21 will beconstant, since the surface of the protective film 21 having theproperties of a conductor or a semiconductor is equipotential, and doesnot depend on the location. For the sake of simplicity, in B of FIG. 6,the ion sheath is represented as a resistor to simulate a current causedby the flow of positive ions into the substrate.

However, in the case that a substrate 10 having a recess on the backsurface thereof is employed, the range of the substrate portion whichfunctions as a dielectric will change as a protective film 11 is etchedover time, and the relative dielectric constant of the capacitor C willalso change. In greater detail, the following occurs. FIG. 7A is aschematic sectional view showing the state of a protective film 11before etching, and FIG. 7B is a schematic sectional view showing thestate in which the range of a protective film 11 is reduced by etching.

Etching of the protective film 11 progresses at a faster rate at theouter edge portion than at the central portion of the protective film11, due to the influence of etching from the horizontal direction.Therefore, the coating area of the protective film 11 is graduallyreduced from the outer edge toward the central portion, as shown inFIGS. 7A and 7B. Accordingly, the surface area of the substrate 10 atwhich electrical potential is equal is different in the case that acovered region R1 at which the protective film 11 is present on thesurface of the substrate is greater than the range of the recess 13 thatexists on the back surface (FIG. 7A) and the case that the coveredregion R1 is smaller than the range of the recess 13 (FIG. 7B). Thereby,a corresponding region R2 (a region of the portion of substrate thatcontributes to etching of the protective film 11 as a capacitor relatedto the surface electrical potential Vs) of the substrate correspondingto the covered region R1 will also be different. In other words, due tothe coated region R1 being reduced, the average dielectric constant ε₂of the corresponding region R2 in the case of FIG. 7B will be less thanthe average dielectric constant ε₁ of the corresponding region R2 in thecase of FIG. 7A as etching progresses (ε₂<ε₁). This is because thepercentage of volume occupied by the recess 13 (vacuum) having a lowerdielectric constant than the material of the substrate will increasewithin the volume of the corresponding region R2 increases as etchingprogresses. As a result, even if the intensity of the bias voltageapplied to the substrate 10 is constant during etching, the surfaceelectrical potential Vs of the protective film 11 increases because thedielectric constant of the corresponding region R2 becomes smaller.

FIG. 8 is a collection of schematic cross sectional diagrams showing thesteps of a conventional method for etching a protective film formed on asubstrate 10 with a recess on the back surface thereof. As mentionedabove, that the surface electrical potential Vs of the protective film11 increases during etching means that the kinetic energy of positiveions X2 entering the protective film 11 will decrease compared to thekinetic energy of the positive ions X2 at the beginning of etching. Inother words, as shown in FIG. 8, the kinetic energy of the positive ionsX2 continues to decrease over a period of time (A through C of FIG. 8)during which the percentage of the recess 13 that occupies thecorresponding region R2 increases, and will be constant during a periodof time (D in FIG. 8) during which the percentage of the recess 13 thatoccupies the corresponding region R2 does not change Note that withrespect to positive ions X1 that enter the surface of the substrateafter the protective film 11 has been removed, the dielectric constantis maintained constant, because transport of electrical charges will notoccur in a region from which the protective film 11 has been removed,and therefore these regions will not necessarily have equal electricalpotential.

As described above, the kinetic energy of the positive ions X2continuously changing during etching is a problem in accurately formingfine patterns on a substrate. In addition, the kinetic energy of thepositive ions X2 decreasing also results in anisotropic etching becomingdifficult. Therefore, it is necessary to enable high quality patterns ofprotrusions and recesses to be formed even in cases that protectivefilms formed on substrates having recesses on the back surfaces thereofare etched.

First Embodiment

A first embodiment of the present disclosure will be described.

FIG. 1 is a collection of schematic cross sectional diagrams showing thesteps of a method for etching a protective film according to a firstembodiment. In addition, FIG. 2A is a schematic plan view showing astate before reduction of a protective film during an etching process,and FIG. 2B is a schematic plan view showing a state after reduction ofthe protective film during the etching process. FIG. 2A illustrates thestate of a protective film 11 corresponding to A of FIG. 1, and FIG. 2Billustrates the state of the protective film 11 corresponding to D ofFIG. 1. FIG. 3 is a graph showing the manner of decrease of a dielectricconstant and the manner of increase of a bias voltage in the firstembodiment.

In the method for etching a protective film 11 of the presentembodiment, a substrate 10 having a protective film 11 formed on a frontsurface and a recess 13 in a back surface opposite the front surface isprepared, a resist pattern 12 is formed on the protective film 11, andthe protective film 11 is etched using plasma while applying a biasvoltage using the resist pattern 12 as a mask, as illustrated in FIG. 1.In the present embodiment, the bias voltage is applied such that itincreases according to the degree of decrease in dielectric constantduring a period of time in which the dielectric constant is decreasing(A through C of FIG. 1), and maintained at a value corresponding to aconstant dielectric constant during a period of time in which thedielectric constant is constant (D of FIG. 1) (FIG. 3). The method forproducing a template of the present embodiment is that in which thesubstrate 10 is etched using the protective film 11, which is etched bythe process described above, as a mask.

(Substrate)

The substrate 10 is a base for a template for nanoimprinting, forexample, and has a recess formed in a surface (back surface) oppositethe surface with a pattern formation region (region in which pattern ofprotrusions and recesses is to be formed). A material having opticaltransparency may be selected for the substrate 10 according to theintended use thereof. The material is not particularly limited and canbe appropriately selected according to the intended use thereof, andexamples of materials include quartz and resin. The substrate 10 is of arectangular shape having a size of 65 mm×65 mm, 5 inches×5 inches, 6inches×6 inches or 9 inches×9 inches, for example. The thickness is alsoselected as appropriate, taking the depth of the recess intoconsideration.

The shape of the recess may be circular, rectangular or polygonal. Thedepth of the recess is designed as appropriate, taking the degree offlexure (bending rigidity) and the gas permeability of the portion ofthe substrate which becomes thin due to recess processing. For example,a substrate having a size of 6 inches×6 inches and a thickness of 6.35mm, having a circular recess with a diameter 63 mm and a depth of 5.25mm (the thickness of the substrate is 1.1 mm at the recess portion)formed in center of the back surface may be utilized.

It is preferable for the substrate 10 to have a stepped structure (a socalled mesa structure) on the surface thereof such that that the patternformation region is on a base (mesa). The presence of the base limitsthe contact region between a template produced by processing thesubstrate 10 and a wafer to the surface of the base when executingnanoimprinting using the template. Therefore, structures (alignmentmarks, for example) which are present on the substrate other than thebase can be prevented from contacting the wafer. The height of thepedestal is preferably within a range from 1 μm to 1000 μm, morepreferably a range from 10 μm to 500 μm, and even more preferably arange from 20 μm to 100 μm.

(Protective Film)

The protective film 11 functions as a hard mask layer, for example. Thematerial of the protective film 11 is selected such that the etchingselectivity of the protective film with respect to resist becomesgreater and such that the etching selectivity of the protective filmwith respect to the subject becomes smaller. It is preferable for thematerial of the protective film 11 to be a metal material such as Cr, W,Ti, Ni, Ag, Pt and Au, metal oxide materials such as CrOx, WO₂ and TiO₂,or composites thereof. It is particularly preferable for the protectivefilm 11 to contain Cr. Taking the etching selectivity of the protectivefilm 11 with respect to the substrate 10 into consideration, it ispreferable for the percentage of a metal material within the constituentmaterial of the protective film 11 to be 40% or greater, more preferably60% or greater, and even more preferably 80% or greater. If the ratio ofthe metal material is too small, the etching selectivity of theprotective film 11 with respect to the substrate 10 will increase. Inaddition, it is preferable for the protective film 11 to have amultilayer structure having at least one layer containing chromium (Cr).

The protective film 11 may be formed by a vapor film forming method suchas sputtering, chemical vapor deposition, molecular beam epitaxy, andion beam sputtering. Then, the transmittance of the protective film 11with respect to light having a wavelength of 365 nm is preferably 30% orgreater, more preferably 50% or greater, and even more preferably 70% orgreater. This is because it will be possible to irradiate the lightthrough the substrate 10 when forming a resist pattern on the protectivefilm 11 by a nanoimprinting method of the photocurable type. Thethickness of the protective film 11 suitably selected taking the aimedprocessing depth, the aforementioned etching selectivity, andpermeability of a substrate to be ultimately obtained, and may be withina range from 1 nm to 30 nm, for example.

(Resist Pattern)

The resist pattern 12 is formed by patterning method such as thenanoimprinting method, the photolithography method, and the electronbeam lithography method. For example, it is possible to form a resistpattern in the following manner using the nanoimprinting method.

The resist material is not particularly limited, and a material preparedby adding a photopolymerization initiator (approximately 2% by mass) anda fluorine monomer (0.1% by mass to 1% by mass) to a polymerizablecompound may be employed. It is also possible to add an antioxidantagent (approximately 1% by mass), if necessary. The material produced bythe above procedure is cured by ultraviolet light having a wavelength ofapproximately 360 nm. In the case that the material has poor solubility,it is preferable for the material to be dissolved by adding a smallamount of acetone or ethyl acetate, and then for the solvent to bedistilled off. Examples of the polymerizable compound include benzylacrylate (Viscoat #160: produced by Osaka Organic Chemical Co., Ltd.),ethyl carbitol acrylate (Viscoat #190: produced by Osaka OrganicChemical Co., Ltd.), polypropylene glycol diacrylate (Aronix M-220:produced by Toagosei Co., Ltd.), trimethylolpropane PO-modifiedtriacrylate (ARONIX M-310: produced by Toagosei Co., Ltd.), and CompoundA represented by Structural Formula (1) below. Further, examples of thepolymerization initiator include alkyl phenone photopolymerizationinitiators such as2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone(IRGACURE 379: produced by BASF Co., Ltd.) and the like. Examples of theabove fluorine monomer include Compound B represented by StructuralFormula (2) below. Here, the viscosity of the material is within a rangefrom 8 cP to 20 cP for example, and the surface energy of the resistmaterial is within a range from 25 mN/m to 35 mN/m, for example.

As the method for coating the resist, it is preferable to use a methodin which a predetermined quantity of liquid droplets can be placed atpredetermined positions on the substrate, such as the ink jet method andthe dispensing method. However, it is possible to use a method capableof applying a resist with a uniform thickness such as the spin coatingmethod or the dip coating method. In the case that the spin coatingmethod or the dip coating method is employed, the resist is diluted witha solvent to be a predetermined thickness. A uniform coated film isformed on the substrate by controlling the rotational speed in the caseof spin coating, and by controlling the draw up speed in the case of thedip coating method.

After the resist is coated on the substrate 10, a mold having apredetermined pattern is caused to contact the resist. It is preferablefor residual gas in the atmosphere between the mold and the substrate tobe reduced by reducing the pressure or by causing the atmosphere to be avacuum prior to the mold being placed in contact with the resist,However, there is a possibility that the resist will volatilize beforecuring in a high vacuum atmosphere, and it may be difficult to maintaina uniform film thickness. Therefore, it is preferable for the residualgas in the atmosphere between the mold and the substrate to be reducedby causing this atmosphere to be a He atmosphere or a reduced-pressureHe atmosphere. Because He passes through quartz substrates, capturedresidual gas (He) will gradually be reduced. A reduced pressure Heatmosphere is more preferable, because the passage of He through quartzis time consuming. It is preferable for the pressure in the reducedpressure atmosphere to be within a range from 1 kPa to 90 kPa, andparticularly preferably within a range from 1 kPa to 10 kPa. After theresist pattern 12 is formed, the mold is peeled off from the resistpattern 12.

(Etching of the Protective Film)

Etching of the protective film 11 is a process of etching the protectivefilm 11 underlying the resist pattern 12, using the resist pattern 12 asa mask. Etching is performed by reactive ion etching using a plasma(RIE). It is preferable for etching to be executed by inductivelycoupled plasma (ICP)-RIE, capacitively coupled plasma (CCP)-RIE orelectron cyclotron resonance (ECR)-RIE. Further, it is preferable for acontrol method that controls the bias power in the present disclosure(electrical power for forming a bias voltage between the plasma and thelower electrode) independent of plasma power (electrical power forforming plasma), in order to facilitate control. The etching conditionsfor etching the protective film 11 are selected such that the etchingselectivity of the protective film 11 with respect to the resist isgreat. This is because the resist mask partially disappears if theselectivity is small, and there is a possibility that break defects(disconnection) will occur.

At least a bias voltage is applied in this process. This is becauseetching does not proceed anisotropically unless a bias voltage isapplied, and an excessive amount of time will be necessary to etch theprotective film 11. In such a case, the resist mask will disappear dueto etching for an excessive amount of time, and break defects willoccur. Even if etching is accomplished without break defects beinggenerated, a significant CD (critical dimension) shift or CD increasecannot be avoided.

Further, in the present disclosure, in order to solve the problemmentioned above, that is, the problem that occurs in the case that aprotective film 11 formed on a substrate 10 having a recess 13 on theback surface thereof is etched, the bias power is increased according tothe manner of decrease in the dielectric constant of the correspondingregion R2 of the substrate corresponding to the covered region R1. Notethat the term “increased” means that the bias voltage is ultimatelyincreased during the etching process from the initiation to thecompletion of etching, and the manner of increase during the etchingprocess is not limited. For example, the bias voltage may becontinuously increased, increased in a stepwise manner, or may beincreased by a combination of these two manners. It is also possible todecrease the bias voltage as necessary during a portion of the etchingprocess.

The present embodiment adopts a method for increasing the bias voltageaccording to the degree of decrease of the dielectric constant while thedielectric constant is decreased, as a method of increasing the biasvoltage (FIG. 3). In other words, while the dielectric constant isdecreasing, the bias voltage is increased in order to offset theincrease in the surface electrical potential Vs caused by the decrease,that is, the bias voltage is increased according to the degree ofdecrease in the dielectric constant. Specifically, the method is asfollows. The percentage of the recess 13 within the corresponding regionR2 increases (A through C of FIG. 1) from a time t₁ (a time when etchingis initiated) to a time t₂ (a time when the range of the covered regionR1 substantially matches the range of the recess 13), and therefore thedielectric constant ε decreases from ε₁ to ε₂. During this time, thebias voltage Vb is gradually increased from V₁ to V₂ so as to offset theincrease in the surface electrical potential Vs caused by the decreasein the dielectric constant in the present embodiment. From the time t₂to a time t₃ (a time when etching is completed), the percentage of therecess 13 within the corresponding region R2 does not change (D in FIG.1), and therefore, the decrease of the dielectric constant ε stops.During this period, the increase in the bias voltage Vb is stopped, andthe bias voltage Vb is maintained at V₂ in the present embodiment.

As a result, the surface electrical potential Vs of the correspondingregion R2 is maintained constant during the etching process, and thekinetic energy of the positive ions X2 is also maintained constant. Theprotective film 11 can be accurately processed while maintaining aconstant etching environment from the initiation to completion ofetching.

Note that FIG. 3 illustrates a case in which the specific dielectricconstant decreases linearly over time as an example. However, the mannerin which the dielectric constant decreases is not limited to that inwhich the decrease is linear over time as in the above example.

It is preferable for a mixed gas of Cl₂ and O₂ to be utilized as anetching gas if the protective film 11 is formed by Cr, and for a mixedgas of Cl₂ and BCl₃ to be utilized as an etching gas if the protectivefilm is formed by Ta.

The range of the covered region R1 during etching may be detected, andthe manner of decrease of the dielectric constant may be determined bythe manner of change in the percentage of the corresponding region R2 ofthe substrate 10 corresponding to the covered region R1 in which therecess 13 is present, for example. Laser beams may be irradiated ontosites on the surface of the substrate 10 during the etching of theprotective film 11, and the range of the covered region R1 can bedetected by detecting the reflected light, for example. Since theposition and size of the recess 13 in the substrate 10 are known, thepercentage of the corresponding region R2 occupied by the recess 13 canbe calculated by detecting the range of the coated region R1 andspecifying the position and size thereof. This percentage may becalculated from the ratio of the volume of the recess 13 with respect tothe volume of the corresponding region R2, for example. Alternatively,if the depth of the recess 13 is constant, the percentage may becalculated by converting a one dimensional ratio of the width W of therecess 13 with respect to the width of the corresponding region R2 to atwo dimensional ratio that also includes depth.

In addition, plasma components may be measured by plasma emissionspectroscopy during etching, and the manner of decrease in dielectricconstant may be determined by the manner of change in the amount of acomponent correlated with etching of the protective film 11 from amongthe measured components, for example. A component which is correlatedwith the etching of the protective film 11 is, for example, a plasmacomponent generated by the material of the protective film 11. Bymeasuring the content or content ratio of such a component in the plasmacomponents, it will be possible to understand to what degree theprotective film 11 has been etched, and it will also be possible tounderstand the degree of reduction of the coated region R1. If thedegree of reduction of the covered region R1 is known, the percentage ofthe corresponding region R2 that corresponds to the covered region R1occupied by the recess 13 may be calculated in the same manner as thatdescribed above.

In addition, with respect to the manner of decrease in dielectricconstant, a manner of increase in bias voltage (a bias voltage controlprofile such as that illustrated in FIG. 3) may be determined in advancebased on the relationship between etching time and the manner ofdecrease in dielectric constant during etching. In this case, the biasvoltage may be increased according to the determined manner of increasein bias voltage.

(Etching of the Substrate)

Etching of the substrate 10 is a process that etches the substrate 10after a pattern is formed in the protective film 11, using theprotective film 11 as a mask. Thereby, a desired pattern of protrusionsand recesses is formed in the substrate 10. The substrate, in which thepattern of protrusions and recesses is formed, is a template. Etching isexecuted by reactive ion etching (RIE) in the same manner as the etchingof the aforementioned protective film 11, for example. It isparticularly preferable for etching to be executed by ICP-RIE, CCP-RIE,or ECR-RIE. Further, it is preferable for a control method that controlsthe bias power in the present disclosure independent of plasma power, inorder to facilitate control.

As described above, the present embodiment increases the bias voltageaccording to the manner of decrease in the dielectric constant of thecorresponding region of the substrate corresponding to the coveredregion of the surface of the substrate at which the protective film ispresent. Therefore, changes in bias voltage at local regions of thesurface of the substrate at which patterns of protrusions and recessesare formed can be predicted appropriately and corrected for. As aresult, it becomes possible to form a high quality pattern ofprotrusions and recesses on a protective film formed on a substratehaving a recess on the back surface thereof.

The method of producing a template of the present embodiment utilizesthe method for etching a protective film described above. Therefore, itbecomes possible to form a high quality pattern of protrusions andrecesses on a protective film formed on a substrate having a recess onthe back surface thereof.

In addition, the template of the present embodiment is produced by theabove method for producing a template. Therefore, the template has ahigh quality pattern of protrusions and recesses.

Second Embodiment

Next, a second embodiment of the present disclosure will be described.The present embodiment differs from the first embodiment in the pointthat a “method in which the bias voltage is set to zero during a periodof time in which the dielectric constant is decreasing, and increased toand maintained at a value corresponding to a constant value of thedielectric constant during a period of time in which the dielectricconstant becomes the constant value” is adopted. Therefore, detaileddescription of constituent elements which are the same as those of thefirst embodiment will be omitted unless particularly necessary.

FIG. 4 is a collection of schematic cross sectional diagrams showing thesteps of a method for etching a protective film according to the secondembodiment. FIG. 5 is a graph showing the manner of decrease of adielectric constant and the manner of increase of a bias voltage in thesecond embodiment.

In the method for etching a protective film 11 of the presentembodiment, a substrate 10 having a protective film 11 formed on a frontsurface and a recess 13 in a back surface opposite the front surface isprepared, a resist pattern 12 is formed on the protective film 11, andthe protective film 11 is etched using plasma while applying a biasvoltage using the resist pattern 12 as a mask, as illustrated in FIG. 4.In the present embodiment, the bias voltage is applied such that it isset to zero during a period of time in which the dielectric constant isdecreasing (A through C of FIG. 4), and increased to and maintained at avalue corresponding to a constant dielectric constant during a period oftime in which the dielectric constant is constant (D of FIG. 4) (FIG.5).

(Etching of Protective Film)

The present embodiment adopts a method in which a bias voltage is notapplied during a period of time in which the dielectric constant isdecreasing, the bias voltage is increased to a value corresponding tothe value of the dielectric constant when the decrease stops, and thebias voltage is maintained at this value (FIG. 5). An ion sheath remainseven if the bias voltage is zero, and therefore positive ions enter theprotective film 11. However, in the present embodiment, the dependencyof the surface electrical potential Vs on time becomes extremely smalleven when the coated region RI is reduced, because the bias voltage iszero. In addition, in the present embodiment, the dielectric constant ofthe corresponding region R2 does not change due to the reduction in thecovered region during the period of time in which the bias voltage isbeing applied, and the kinetic energy of the positive ions X2 that enterthe protective film 11 also does not change. In this case, a biasvoltage is not applied during a period of time from time t₁ to time t₂,and isotropic etching is executed as a result. However, anisotropicetching is executed during a period of time from time t₂ to time t₃.That is, the method of the present embodiment is effective in the casethat it is desired to simplify a control profile or to shorten theperiod of time during which a bias voltage is applied as much aspossible, because the control profile of a bias voltage will becomecomplex if a bias voltage is applied while the dielectric constant isdecreasing. There is also an advantage that break defects will becomeunlikely to occur if the amount of time during which a bias voltage isapplied is shortened.

As a result, the surface electrical potential Vs of the correspondingregion R2 is maintained constant during the etching process, and thekinetic energy of the positive ions X2 is also maintained constant. Theprotective film 11 can be accurately processed while setting the etchingenvironment in two steps, which is easily controlled, from theinitiation to completion of etching.

As described above, in the present embodiment as well, the bias voltageis increased according to the manner of decrease in the dielectricconstant of the corresponding region of the substrate corresponding tothe covered region of the surface of the substrate at which theprotective film is present. Therefore, the same advantageous effects asthose obtained by the first embodiment are obtained.

EXAMPLES

Examples of the present disclosure are shown below.

Example 1 (Production of Mold)

A resist solution having a PHS (polyhydroxy styrene) series chemicallyamplified resist as a main component was coated on a Si substrate by thespin coating method to form a resist layer. Then, an electron beam wasirradiated while scanning the Si substrate on a XY stage, and the entiresurface of the resist layer having a range of 20×30 mm was exposed.Then, the resist layer was developed, the exposed portions were removed,and the pattern of the resist layer was employed as a mask to performselective etching by RIE such that the depth of grooves was 100 nm byRIE, to obtain a Si mold. The taper angle of the pattern was 85 degrees.A mold release process was administered on the surface of the mold by adip coating process with OPTOOL DSX. The pattern at the center of the Sisubstrate has a 10 mm square transfer surface region, and a pattern ofprotrusions and recesses is a line pattern having a length of 10 mm, awidth of 28 nm, and grooves having a pitch 56 nm and a depth of 60 nm.

(Substrate for Nanoimprinting)

A 152 mm square quartz substrate having a thickness of 6.35 mm wasutilized as a nanoimprinting substrate. A 26×32 mm rectangular basehaving a height of 30 μm is formed on a transfer region at the center ofthe quartz substrate by wet etching. Further, a recess having a diameter64 mm and a depth of 5 mm is formed in the center of the back surface ofthe substrate. A 4 nm thick chromium film was formed on the surface ofthe substrate by the sputtering method to form a hard mask layer.

Thereafter, the substrate underwent a surface treatment with a silanecoupling agent KBM-5103 (produced by Shin Etsu Chemical Co., Ltd.),which has superior adhesive properties with resist. KBM-5103 was dilutedto 1% by mass with PGMEA, then coated on the surface of the substrate bythe spin coating method. Next, the coated substrate was annealed on ahot plate at 150° C. for 5 minutes, to bind the silane coupling agent tothe surface of the substrate.

(Nanoimprinting Process)

A resist including 48% by mass of Compound A described above, 48% bymass of Aronix M220, 3% of IRGACURE 379 and 1% by mass of compound B wasprepared. Next, the photocurable resist was coated on the chromium filmof the quartz substrate. DMP-2838, which is a piezo type ink jet printerproduced by FUJIFILM Dimatix, Inc., was utilized to coat the resist.DMC-11610, which is a dedicated 10 pl head, was utilized as the ink jethead. Droplet discharge conditions were set and adjusted in advance suchthat the amount in each droplet was 10 pl. The droplet arrangementpattern was a lattice pattern with a pitch of 450 μm. Droplets werearranged on the transfer region (the base on the substrate) according tothe droplet arrangement pattern.

The mold and the quartz substrate were caused to approach each other toa position at which a gap therebetween is 0.1 mm or less, and the twowere aligned from the back surface of the quartz substrate such thatalignment marks on the substrate and alignment marks on the mold werealigned. The space between the mold and the quartz substrate wasreplaced with 99% or greater by volume of He gas, and pressure wasreduced to 50 kPa or lower after the replacement with He. The mold wascaused to contact the droplets of resist under reduced pressure Heconditions. After contact, 1 Mpa of pressure was applied for 5 seconds,and exposure was performed with ultraviolet light having a wavelength of365 nm at an irradiation intensity of 300 mJ/cm² to cure the resist.Thereafter, the mold and the substrate were separated.

(Etching of Hard Mask Layer)

An inductively coupled plasma (ICP) reactive ion etching apparatus wasemployed to etch the hard mask with the etching conditions shown below.

Gas species chlorine:oxygen = 3:1 Process pressure 5 Pa ICP power(plasma power) 100 W Over etching amount 50%

Regarding the bias power, the bias power was increased from 5 W at aconstant rate accompanying the passage of time from initiation ofetching, based on the etching time and the area of the covered region ofthe hard mask layer, which was measured in advance. At a point in timeat which the covered region of the hard mask layer was approximately thesame as the range of the recess in the substrate, the bias power wasadjusted to be 40 W, and etching was performed while maintaining thebias power at 40 W from this point in time.

The endpoint of the execution time of the etching process was designatedas a point in time which is 50% more than the time elapsed until atleast the hard mask layer was removed. That is, the etching process wasexecuted with a point in time at which the over etching amount became50% of the average thickness of the hard mask layer as a guide.

(Etching of Substrate)

The quartz substrate was etched with the hard mask layer as a maskaiming for a depth of 60 nm under the following conditions.

Gas species CHF₃:argon = 1:10 Process pressure 1 Pa ICP power 100 W Biaspower 100 W

(Evaluation of Pattern)

Thereafter, the shape of the pattern was evaluated by a scanningelectron microscope.

Evaluation Item 1

The pattern was evaluated as “GOOD” if there were no break defects, andevaluated as “POOR” if break defects were present.

Evaluation Item 2

With respect to CD shift, an amount of deviation from a line width of 28nm was evaluated. A case in which the deviation was within a range of28±3 nm was evaluated as “GOOD”, and a case in which the deviation wasoutside this range was evaluated as “POOR”.

Example 2

Example 2 is the same as Example 1 except that the etching process ofthe hard mask layer was executed in the following manner. Specifically,in Example 2, an inductively coupled plasma (ICP) reactive ion etchingapparatus was employed to etch the hard mask with the etching conditionsshown below.

Gas species chlorine:oxygen = 3:1 Process pressure 5 Pa ICP power 100 WOver etching amount 50%

Regarding the bias power, the bias power was maintained at zero for acertain amount of time from initiation of etching, based on the etchingtime and the area of the covered region of the hard mask layer, whichwas measured in advance. At a point in time at which the covered regionof the hard mask layer was approximately the same as the range of therecess in the substrate, the bias power was adjusted to be 40 W, andetching was performed while maintaining the bias power at 40 W from thispoint in time.

Comparative Example 1

Comparative Example 1 is the same as Example 1 except that the etchingprocess of the hard mask layer was executed in the following manner.Specifically, in Comparative Example 1, an inductively coupled plasma(ICP) reactive ion etching apparatus was employed to etch the hard maskwith the etching conditions shown below.

Gas species chlorine:oxygen = 3:1 Process pressure 5 Pa ICP power 100 WBias power 40 W Over etching amount 50%

Comparative Example 2

Comparative Example 2 is the same as Example 1 except that the etchingprocess of the hard mask layer was executed in the following manner.Specifically, in Comparative Example 2, an inductively coupled plasma(ICP) reactive ion etching apparatus was employed to etch the hard maskwith the etching conditions shown below.

Gas species chlorine:oxygen = 3:1 Process pressure 5 Pa ICP power 100 WBias power 0 W Over etching amount 50%

Comparative Example 3

Comparative Example 3 is the same as Example 1 except that the etchingprocess of the hard mask layer was executed in the following manner.Specifically, in Comparative Example 3, an inductively coupled plasma(ICP) reactive ion etching apparatus was employed to etch the hard maskwith the etching conditions shown below.

Gas species chlorine:oxygen = 3:1 Process pressure 5 Pa ICP power 100 WBias power 0 W Over etching amount 200%

Evaluation

Table 1 shows the evaluation results for Examples 1 and 2 as well as forComparative Examples 1 through 3. None of Comparative Examples 1 through3 exhibited evaluations equivalent to those of Examples 1 and 2, and thesuperiority of the present disclosure was demonstrated.

TABLE 1 BREAK DEFECTS CD SHIFT Example 1 GOOD GOOD Example 2 GOOD GOODComparative Example 1 POOR GOOD Comparative Example 2 GOOD POORComparative Example 3 POOR GOOD

What is claimed is:
 1. A method for etching a protective film,comprising the steps of: preparing a substrate having a protective filmformed on a front surface and a recess in a back surface opposite thefront surface; forming a resist pattern on the protective film; andetching the protective film using plasma while applying a bias voltage,using the resist pattern as a mask; the bias voltage being increasedaccording to the manner of decrease in the dielectric constant of aregion of the substrate corresponding to a covered region of the frontsurface at which the protective film is present in the protective filmetching step.
 2. A method for etching a protective film as defined inclaim 1, wherein: the bias voltage is increased according to a degree ofdecrease in the dielectric constant while the dielectric constant isdecreasing, and maintained at a value corresponding to a constant valuewhile the dielectric constant is at the constant value.
 3. A method foretching a protective film as defined in claim 1, wherein: the biasvoltage is zero while the dielectric constant is decreasing, thenincreased to and maintained at a value corresponding to a constant valuewhile the dielectric constant is at the constant value.
 4. A method foretching a protective film as defined in claim 1, wherein: the range ofthe covered region is detected during etching; and the manner ofdecrease in the dielectric constant is determined based on the manner ofchange in the percentage of the recess within the region of thesubstrate corresponding to the covered region.
 5. A method for etching aprotective film as defined in claim 1, wherein: plasma components aremeasured by plasma emission spectroscopy during etching; and the mannerof decrease of the dielectric constant is determined based on the mannerof change in the amount of a component which is correlated with etchingof the protective film from among the measured components.
 6. A methodfor etching a protective film as defined in claim 1, wherein: the mannerof increase of the bias voltage is determined in advance based on therelationship between etching time and the manner of decrease of thedielectric constant during etching; and the bias voltage is increasedaccording to the determined manner of increase of the bias voltage.
 7. Amethod for etching a protective film as defined in claim 1, wherein: thepercentage of metal materials within the constituent material of theprotective film is 40% or greater.
 8. A method for etching a protectivefilm as defined in claim 1, wherein: the transmittance of the protectivefilm with respect to light having a wavelength of 365 nm is 30% orgreater.
 9. A method for producing a mold, comprising: etching aprotective film formed on a substrate having a recess on the backsurface thereof by a method for etching a protective film as defined inclaim 1; and etching the substrate using the etched protective film as amask.
 10. A mold produced by the method for producing a mold as definedin claim 9.